oidtree: add ability to store data

The oidtree data structure is currently only used to store object IDs,
without any associated data. So consequently, it can only really be used
to track which object IDs exist, and we can use the tree structure to
efficiently operate on OID prefixes.

But there are valid use cases where we want to both:

  - Store object IDs in a sorted order.

  - Associated arbitrary data with them.

Refactor the oidtree interface so that it allows us to store arbitrary
payloads within the respective nodes. This will be used in the next
commit.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

loose.c

@@ -57,7 +57,7 @@ static int insert_loose_map(struct odb_source *source,
 	inserted |= insert_oid_pair(map->to_compat, oid, compat_oid);
 	inserted |= insert_oid_pair(map->to_storage, compat_oid, oid);
 	if (inserted)
-		oidtree_insert(files->loose->cache, compat_oid);
+		oidtree_insert(files->loose->cache, compat_oid, NULL);
 
 	return inserted;
 }

object-file.c

@@ -1857,6 +1857,7 @@ static int for_each_object_wrapper_cb(const struct object_id *oid,
 }
 
 static int for_each_prefixed_object_wrapper_cb(const struct object_id *oid,
+					       void *node_data UNUSED,
 					       void *cb_data)
 {
 	struct for_each_object_wrapper_data *data = cb_data;
@@ -2002,7 +2003,7 @@ static int append_loose_object(const struct object_id *oid,
 			       const char *path UNUSED,
 			       void *data)
 {
-	oidtree_insert(data, oid);
+	oidtree_insert(data, oid, NULL);
 	return 0;
 }
 

oidtree.c

@@ -9,6 +9,7 @@
 struct oidtree_node {
 	struct cb_node base;
 	struct object_id key;
+	void *data;
 };
 
 void oidtree_init(struct oidtree *ot)
@@ -25,29 +26,42 @@ void oidtree_clear(struct oidtree *ot)
 	}
 }
 
-void oidtree_insert(struct oidtree *ot, const struct object_id *oid)
+struct oidtree_data {
+	struct object_id oid;
+};
+
+void oidtree_insert(struct oidtree *ot, const struct object_id *oid,
+		    void *data)
 {
 	struct oidtree_node *on;
+	struct cb_node *node;
 
 	if (!oid->algo)
 		BUG("oidtree_insert requires oid->algo");
 
 	on = mem_pool_alloc(&ot->mem_pool, sizeof(*on));
 	oidcpy(&on->key, oid);
+	on->data = data;
 
 	/*
 	 * n.b. Current callers won't get us duplicates, here.  If a
 	 * future caller causes duplicates, there'll be a small leak
 	 * that won't be freed until oidtree_clear.  Currently it's not
 	 * worth maintaining a free list
 	 */
-	cb_insert(&ot->tree, &on->base, sizeof(*oid));
+	node = cb_insert(&ot->tree, &on->base, sizeof(*oid));
+	if (node) {
+		struct oidtree_node *preexisting = container_of(node, struct oidtree_node, base);
+		preexisting->data = data;
+	}
 }
 
-bool oidtree_contains(struct oidtree *ot, const struct object_id *oid)
+static struct oidtree_node *oidtree_lookup(struct oidtree *ot,
+					   const struct object_id *oid)
 {
 	struct object_id k;
 	size_t klen = sizeof(k);
+	struct cb_node *node;
 
 	oidcpy(&k, oid);
 
@@ -58,7 +72,20 @@ bool oidtree_contains(struct oidtree *ot, const struct object_id *oid)
 	klen += BUILD_ASSERT_OR_ZERO(offsetof(struct object_id, hash) <
 				offsetof(struct object_id, algo));
 
-	return !!cb_lookup(&ot->tree, (const uint8_t *)&k, klen);
+	node = cb_lookup(&ot->tree, (const uint8_t *)&k, klen);
+	return node ? container_of(node, struct oidtree_node, base) : NULL;
+}
+
+bool oidtree_contains(struct oidtree *ot, const struct object_id *oid)
+{
+	struct oidtree_node *node = oidtree_lookup(ot, oid);
+	return node ? 1 : 0;
+}
+
+void *oidtree_get(struct oidtree *ot, const struct object_id *oid)
+{
+	struct oidtree_node *node = oidtree_lookup(ot, oid);
+	return node ? node->data : NULL;
 }
 
 struct oidtree_each_data {
@@ -82,7 +109,7 @@ static int iter(struct cb_node *n, void *cb_data)
 			return 0;
 	}
 
-	return data->cb(&node->key, data->cb_data);
+	return data->cb(&node->key, node->data, data->cb_data);
 }
 
 int oidtree_each(struct oidtree *ot, const struct object_id *prefix,

oidtree.h

@@ -29,18 +29,26 @@ void oidtree_init(struct oidtree *ot);
  */
 void oidtree_clear(struct oidtree *ot);
 
-/* Insert the object ID into the tree. */
-void oidtree_insert(struct oidtree *ot, const struct object_id *oid);
+/*
+ * Insert the object ID into the tree and store the given pointer alongside
+ * with it. The data pointer of any preexisting entry will be overwritten.
+ */
+void oidtree_insert(struct oidtree *ot, const struct object_id *oid,
+		    void *data);
 
 /* Check whether the tree contains the given object ID. */
 bool oidtree_contains(struct oidtree *ot, const struct object_id *oid);
 
+/* Get the payload stored with the given object ID. */
+void *oidtree_get(struct oidtree *ot, const struct object_id *oid);
+
 /*
  * Callback function used for `oidtree_each()`. Returning a non-zero exit code
  * will cause iteration to stop. The exit code will be propagated to the caller
  * of `oidtree_each()`.
  */
 typedef int (*oidtree_each_cb)(const struct object_id *oid,
+			       void *node_data,
 			       void *cb_data);
 
 /*

t/unit-tests/u-oidtree.c

@@ -19,7 +19,7 @@ static int fill_tree_loc(struct oidtree *ot, const char *hexes[], size_t n)
 	for (size_t i = 0; i < n; i++) {
 		struct object_id oid;
 		cl_parse_any_oid(hexes[i], &oid);
-		oidtree_insert(ot, &oid);
+		oidtree_insert(ot, &oid, NULL);
 	}
 	return 0;
 }
@@ -38,9 +38,9 @@ struct expected_hex_iter {
 	const char *query;
 };
 
-static int check_each_cb(const struct object_id *oid, void *data)
+static int check_each_cb(const struct object_id *oid, void *node_data UNUSED, void *cb_data)
 {
-	struct expected_hex_iter *hex_iter = data;
+	struct expected_hex_iter *hex_iter = cb_data;
 	struct object_id expected;
 
 	cl_assert(hex_iter->i < hex_iter->expected_hexes.nr);
@@ -105,3 +105,23 @@ void test_oidtree__each(void)
 	check_each(&ot, "32100", "321", NULL);
 	check_each(&ot, "32", "320", "321", NULL);
 }
+
+void test_oidtree__insert_overwrites_data(void)
+{
+	struct object_id oid;
+	struct oidtree ot;
+	int a, b;
+
+	cl_parse_any_oid("1", &oid);
+
+	oidtree_init(&ot);
+
+	oidtree_insert(&ot, &oid, NULL);
+	cl_assert_equal_p(oidtree_get(&ot, &oid), NULL);
+	oidtree_insert(&ot, &oid, &a);
+	cl_assert_equal_p(oidtree_get(&ot, &oid), &a);
+	oidtree_insert(&ot, &oid, &b);
+	cl_assert_equal_p(oidtree_get(&ot, &oid), &b);
+
+	oidtree_clear(&ot);
+}